Girdling effect on fruitlets hormonal and nutritional content in different Citrus shoot types

Abstract

In this paper we studied the effect of branch girdling on fruitlets abscission arising from different shoot types, and its relationship with abscisic acid (ABA) and carbohydrates content in adult trees of ‘Clemenules’ mandarin (Citrus reticulata Blanco). Besides, girdling combined with two gibberellin inhibitors of phases I and II (Cycocel and Paclobutrazol), was evaluated by recording total crop at harvest. Both growth inhibitors reduced crop by 40% whereas in combination with girdling reached the level of control trees. Paralleling this effect, PBZ reduced total carbohydrates content in young fruitlets, whereas combined with girdling, within 30 days of treatment, carbohydrates level were restores to that of control trees. Concomitantly, girdling reduced by more than 60 % ABA content in fruitlets at seven days after treatment, following a similar trend in both types of shoots. This decrease in ABA level was followed by a reduction in the rate of fruitlets abscission, which remained at levels significantly lower for the type of shoots studied until 60 days after treatment. Final fruit set of leafless inflorescences was not affected by girdling, whereas leafy inflorescence reduced abscission at the end of physiological fruit drop. Thus, the present work reveals that girdling can improve fruit set by early modifications of carbohydrates and GAs/ABA relationship regardless of shoot type.